Related Party Transactions - Additional Information (Details) - USD ($)		4 Months Ended
Jun. 30, 2021	Jun. 30, 2021	Mar. 31, 2021
Related Party Transaction [Line Items]
Outstanding balance of related party note	$ 167,251	$ 167,251
Advances from related parties	0	150,000
Working capital loans warrant
Related Party Transaction [Line Items]
Outstanding balance of related party note	0	0	$ 0
Loan conversion agreement warrant	$ 1,500,000	$ 1,500,000
Price of warrant	$ 1.50	$ 1.50
Promissory Note with Related Party
Related Party Transaction [Line Items]
Maximum borrowing capacity of related party promissory note	$ 300,000	$ 300,000
Outstanding balance of related party note	$ 167,251	$ 167,251	$ 150,000

Price per share or per unit of warrants or rights outstanding.

No definition available.

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Namespace Prefix:	mtal_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of maximum borrowing capacity of related party promissory note.

+ References

No definition available.

+ Details

Name:	mtal_MaximumBorrowingCapacityOfRelatedPartyPromissoryNote
Namespace Prefix:	mtal_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The maximum amount which a potential loan could have repaid through issuance of warrants.

+ References

No definition available.

+ Details

Name:	mtal_MaximumLoansConvertibleIntoWarrants
Namespace Prefix:	mtal_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amounts of proceeds advances from related parties.

+ References

No definition available.

+ Details

Name:	mtal_ProceedsAdvancesFromRelatedParties
Namespace Prefix:	mtal_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount for notes payable (written promise to pay), due to related parties.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.17)
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(k)(1))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_RelatedPartyTransactionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_ClassOfWarrantOrRightAxis=mtal_WorkingCapitalLoansWarrantMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=mtal_PromissoryNoteWithRelatedPartyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: